According to German AS No. 1 086 876, a knife-ring cutter of the type for disintegrating wood chips has become known. A stationary, cylindrical knife-ring is tipped hereby on its inner periphery at even distances with exchangeable regrindable knives. A chip feeder with secantially arranged moving arms and adjustable striking bars (counterknives) rotates inside the knife-ring. Through the action of the air stream which is sucked in by the air blades and of centrifugal force, the chips are moved in a direction substantially parallel to the fibers therein in front of the knife blades, in such a manner that they are divided into thin flakes along the direction of the fibers therein. Known furthermore are knife-ring cutters with a stationary, conical knife-ring (compare German Pat. No. 16 53 098 and German OS No. 24 20 189).
Finally German Pat. No. 26 39 123 suggests a method and a corresponding apparatus in which the chips, which along their fiber direction are at least twice as long as the length of the flakes which are supposed to be manufactured therefrom, are disintegrated into flakes, the chip length of which is defined for which strip knives with additional chipping edges or strip knives which are tipped with chipping noses are supposed to be used.
In the above-mentioned apparati, knife blades and rotating counterknives can be arranged parallel to the axis of rotation or at an angle thereto. In the case of an angular arrangement, the cutting knives apply a slanted cut, which is also identified as a diagonal cut.
The mentioned apparati (knife-ring cutters) have in common that their knives at the end of their cutting edge life (i.e. when dull) must be dismounted, reground and thereafter again installed, all of which is time consuming. Even if corresponding with German AS No. 26 28 773 at the end of an edge life, the complete knife-ring is dismounted and is replaced with a knife-ring with sharp knives, this still leaves it necessary to exchange, outside of the apparatus, all dull knives with sharpened knives.
As blade dulling progresses, energy consumption of the apparatus increases, while at the same time the chip cutting flake quality drops. Thus, there have been many efforts to improve the chip cutting quality. Knife-ring cutters, in which cutting knife and counterknife are arranged at a certain diagonal-cut angle to one enother to achieve a slicing cut which is advantageous for the chip quality, produce at the start of an edge life considerably better flakes than knife-ring cutters in which cutting knife and counterknife are axially parallel. Said diagonal cut, however, causes the packing density of the chips to increase toward the trailing knife end. The consequence is that the knives become considerably more quickly dull in this area. In the case of knife-ring cutters with axially parallel cutting knives and counterknives, the chip quality is not so high at the start of cutting, but the load on the knives is more uniform and wear is not so quick. However, the influence on the chip quality and energy consumption due to more frequent knife exchange has narrow limits, not only for reasons of cost, but also because the percentage portion of chips which are too thick and are torn and are produced at the start of an edge life with "overly sharp" knives increases to the same degree as the running time of the knife is shortened. In addition, it is often not permissible in industrial practice to simply switch off a knife-ring cutter with dulled knives. During a chip shortage, which occurs particularly often during the winter, cutting must be continued without consideration for the chip quality and energy consumption because otherwise the entire production would come to a halt. However, especially during the cold time of the year, the knives must be exchanged considerably more often, because strongly frozen chips which have mixed with them sand or frozen-on stones reduce the edge life of a set of knives often to a few minutes, which is disadvantageous for chip production.
Thus the basic purpose of the invention is to provide a method with the help of which, independent from the condition of the supplied chips, flakes of an always constant quality and homogeneity are produced, in that the factors "chip quality" and "energy consumption" are brought preselectably into a relation which corresponds with the economical and technological demands. The apparatus for carrying out the method is intended to be constructed to assure uninterrupted operation over a time period which is as long as possible.
This purpose is attained by the invention with a method, in which blade portions of a long strip-steel knife, which blade portions are in use, have over the full operating time always the same medium sharpness. For limiting the chip lengths, the blades of the strip-steel knives can be provided with integrated chipping edges, for example corresponding with those shown in U.S. Pat. No. 3,866,643 or German OS No. 32 28 852. The apparatus which is utilized for carrying out the method uses a chip cutter of the general known kind having a stationary, cylindrical knife-ring and therein installed, a rotating chip conveying mechanism for fiber-parallel chip forced feed, which conveyor mechanism is tipped with counterknives preferably arranged at a diagonal-cut angle with respect to the strip-steel knives and therefore with correspondingly concave-shaped or spiral-shaped counter-knives. The knife-ring is provided at symmetrical distances on its inner periphery with knife-clamping devices. Each knife clamping device includes clamping plate. Each clamping plate is tightened preferably by a conventional center clamping (tightening) means. Strip-steel knives which are ground on one side or on both sides are advanced, either continuously for periodically on a timed basis, between said clamping plates. The length of one strip-steel knife corresponds at least to the single, but preferably to a multiple of the cutting blade portion actually in use. The advance (feed) of the strip-steel knives can be made easier by the knives having on both sides of their longitudinal axis pressed-in recesses, into which enters a corresponding feed mechanism. In addition, a corresponding lubricant can be applied onto the strip steel. The strip-steel knives can at a suitable length also be pulled through between their clamping plates. Each strip-steel knife can be of great length (in effect of endless length) and unwound from a roller into position between its clamping plates from which the dulled portion of the knife is wound onto a further roller on the output side of the clamping plates. Alternatively each strip-steel knife can be fed to its clamping plates in shorter individual lengths which correspond with a part or a single or multiple length of the blade section in use. In a preferred embodiment such blade lengths are stored stacked in a magazine, from where they are fed by a corresponding feed-in or pull-through mechanism to a respective pair of clamping plates. Alternatively a universal (common or central) magazine can be arranged movably such that all strip-steel knives can be fed successively to successive pairs of clamping plates. Finally, in the case of a stationary universal magazine, the knife-ring can be supported rotatably in a conventional manner in order to make possible in this manner the loading of the knife-ring with new strip-steel knives.
In order to exactly maintain the desired knife protrusion it is possible for example to provide strip-steel turning knives with a conventional through-going centering groove, into which engage spring, which are received in one of the two clamping plates. In strip-steel turning knives according to German OS No. 32 28 852 it is also possible to utilize the rearward chipping edges, which are not in engagement with the chips, as stop surfaces. In the case of strip-steel knives ground sharp only on the front edge the back edge of the knife can be used for a stop surface.
Corresponding with the inventive method, the continuous or timed (periodic) advancing of the strip-steel knives occurs dependent on time or dependent on apparatus energy consumption level. In the case of an timed feed, the central clamping means for all knives is designed to provide two different clamping stages force levels, as follows. A weaker clamping stage 1 makes the timed infeed or pull-through of the strip-steel knives easier. Immediately after the end of one cycle, clamping stage 2 is switched on, which applies a higher contact pressure. In the preferred embodiment of the inventive apparatus with knife arrangement for diagonal cut, knife infeed occurs from the machine side where the chips to be cut have the greatest packing density, so that the respectively sharper blade section lies always in the zone of the greatest blade wear rate (stress). In the case of axially arranged strip-steel knives, and counterknives which are arranged thereto for diagonal cut, the cutting edge of the counterknife is constructed such that, due to its concave or spiral-shaped construction it has over its full length always the same distance from the cutting edges of the strip-steel knives.